Treatment of pitch



Sept. 22, 1953 K. A. SMITH ET AL 2,652,593

TREATMENT OF PITCH Filed Jan. 31, 1951 INVENTOR Kenneth A.Smith Donclld K. Hedeen ATTO R N EY Patented Sept. 22, 1953 TREATMENT OF PITCH Kenneth A. Smith, Park Forest, and Donald K. Hedeen, Markham, Ill., minors to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application January 31, 1951, Serial No. 208,742 3 Claims. (01. 18-473) Our invention relates to the water quenching of hot molten petroleum pitch to produce a solid pitch conveniently adapted to conventional methods of storage and transportation. Our invention is useful in the disposal of waste pitch produced in the conversion of heavy petroleum oils. More particularly, our invention finds special utility in the pitching process, described in the applications for United States Patents, Serial Nos. 136,069 and 135,427, filed on December 28, 1949, by Harry L. Pelzer, and by Leroy K. Cheney, respectively, by providing a means for converting the pitch produced therein to a form compatible with commercial handling methods whereby the pitch may be readily transported to a point of use or storage.

The current production of heavy petroleum residual products vastly exceeds the natural demand for such residua in any form. I The before noted copending applications describe a process of pitching which increases the recovery of more desirable hydrocarbons from such residua, but which is, itself, accompanied by a large production of petroleum pitch. The problem of the disposal of such pitch is enhanced by almost complete lack of utility as such in quantity, since it is obtained in the liquid state at temperatures usually in excess of 500 or 600 F. and ranging upwards to 900 F. or more. Moreover, petroleum pitch has a softening point (B & B) which is of the order of 200 to 400 F. and, consequently, cannot be conveniently transported by pipe lines of any extended length without heavy insulation and expensive reheating requirements in order to maintain it in fluid condition. In addition, liquid pitch cannot be kept at temperatures neeessary to maintain it in the liquid state for excessive lengths of time, as it is subject to coking and tar separation whereby the pipe lines and other vessels carrying such liquid pitch become plugged. As a consequence of these considerations, any means for solidifying the pitch, of necessity, must be located in the proximity of the pitching unit. Furthermore, the high softening point of the material prohibits conventional tank storage.

It has seemed necessary to dump the liquid pitch at some convenient location such as in a lake or on an open field. But, as the material cannot be dumped at one location continuously for any extended period of time, unless unlimited space is available, such procedure provides only a temporary solution. Ultimately, a new loca tion must be found or the solid mass of pitch must be removed by blasting or other equally impractical means. Since extended pipe lines are not commercially feasible, eventually the pitching unit must be closed down for lack of space in which to dump pitch.

The desirable solution of theproblem is obviously a means by which hot liquid pitch may be cooled, solidified and fragmented so that it may easily be handled by conventional conveyors, elevators and other methods of transportation. It is even more desirable that the fragmented pitch should have some utility of itself, for example, as a fuel. It is to these ends that our invention is specifically directed.

By reason of the quantities of pitch which must be handled by any practical cooling means adaptable to commercial operation, water appears to be the most feasible coolant from an economic standpoint.

Several previous proposals have been made using water as a coolant.

It has been proposed to use a water-cooled drum flaking unit to produce a flaked solid pitch. Such means are satisfactory in small scale operation, but are not practical when commercial scale production is contemplated, as equipment costs and size become prohibitive. For example, for such a unit to handle 10 barrels of fluid pitch per hour, a relatively small quantity in a commercial sense, requires a pair of drums 10 feet by 10 feet. Moreover, vast amounts of power are consumed in rotating the drums against the flaking edge in order to overcome the strong adhesion of the solid pitch to the It has been proposed to effect cooling by water sprays directed against liquid pitch on a flexible steel conveyor belt. To operate such a system. satisfactorily, even at the low pitch rate of 10 barrels per hour, would require a flexible steel belt conveyor or inches width. The largest such unit which appears to be available at this date is only 72 inches long. Again. the equipment size and cost required in co m 1-: ercial operation is excessive.

We have found that hot liquid pitch can be economically and practicably quenched with water on a commercial scale by injecting precooled liquid pitch into a body of water beneath the surface of such water. Such injection must effect a wide dispersion of the liquid pitch before it has had substantial contact with the water coolant. We accomplish this by pumping the liquid pitch into the body of water while dispersing the pitch at point of discharge by means of compressed air. The pitch is simultaneously quenched and fragmented.

It has before been proposed to cool liquid pitch by direct contact with a body of water. Such methods to this time have been unsatisfactory because the product is friable and bulky with low apparent density, has a multitude of pores, and is accompanied by a large production of fines. Such solid fragments as are produced quickly crumble when handled by conventional equipment such as conveyors and elevators. The fine particles are extremely difficult to dry, and tend to clog standard mechanical handling equipment, causing chain drives to jump their sprockets, screw conveyors to jam and similar difficulties.

Moreover, hot, fluid pitch is lighter than water, and, when injected below water, forms large chunks which float to the surface of the water. The surfaces of these chunks cool and harden to form thin, tenacious, rubber-like coatings which are inefficient conductors of heat, while the interiors of the large chunks remain in the liquid state. Such heat as is transmitted through the surface coatings of the chunks to the water generates steam which ruptures some of the chunks and causes the entire surface of the water to become covered with a blanket of pitch which solidifies only where it contacts water. Further contact produces more steam which causes the blanket to froth and solidify ultimately in a sponge-like mass.

Mechanical agitation of the pitch as it is injected into water serves only to cover the paddles or other agitating apparatus with a tarry adherent which retards or prevents further agitation by increased resistance and clogging of any parts having close tolerances.

It is indeed surprising in view of these considerations to find that pitch may be quenched by under-water injection, yet we have found it possible to do so without excessive equipment cost or size. Moreover, the pitch produced when using our method and apparatus has substantially even fragment size, high density, and is non-friable. The fragments formed are smooth, hard, glassy-like pellets which are particularly useful as a solid bituminous fuel, are easily dried and do not crumble when subjected to the rough handling of a screw conveyor.

We have found it is essential to fragment the pitch into dispersed particles of small size, as it is injected into the water coolant. This is accomplished by pumping the liquid pitch into a body of the water coolant and dispersing it by means of compressed air under sufficient pressure to create a turbulent condition at the point of pitch injection. Thus the pitch is given sufficient area to contact with the coolant to permit its solidification in small fragments, during the period in which the pitch fragments are in contact with the coolant. Failure to disperse and fragment the pitch results in the production of a spongy mass, as described before.

It is also essential to the production of hard particles of pitch, as described above, that, prior to introducing the liquid pitch into the body of water, it be cooled to a temperature between the softening point temperature of the pitch and the temperature at which the density of the liquid pitch is equal to that of the coolant water. Failure to pre-cool the liquid pitch results in a soft, porous product, produces a less even fragment size and causes a large production of fines and floaters.

The drawings illustrate an apparatus which is adapted to carry out our invention.

Figure 1 is a sectional elevation of such apparatus.

Figure 2 is a plan view of the apparatus shovm in Figure 1.

Figure 3 is an end view of the apparatus shown in Figure 1, as seen from the left-hand side of the view in Figure 1.

Figures 4 and 5 are respectively a sectional elevation, and an end view of a pitch injector suit- 4 able for use with the apparatus shown in Figures 1, 2 and 3. I

In the drawings the reference numeral I, designates an open surfaced tank adapted to contain a body of coolant water. Tank I, comprises an end wall 2, side walls 3 and 4 and bottom plates I and 6; this tank has an appearance of a V-bot tomed, perpendicularly walled, trough in which the bottom and sides incline upwardly and inwardly, respectively, toward one end of the tank.

End wall 2 is suitably provided with a water outlet 1, to maintain a proper water level within tank I. Pitch injectors 8, are mounted in end wall 2 below the surface of the coolant water, advantageously at a depth sufficient to provide space for turbulence resulting from the pitch injection.

Figures 4 and 5 show in detail the structure of pitch injectors 8, each of which comprises two coaxially positioned cones 9 and I0 joined at their bases by annular disk II, and truncated at their respective apices to form holes I2 and I3. Pitch entry line I4, engages at its end with hole I2. Spider support I5 is provided to support line I4 with respect to injector 8 and spider support I6 is provided to support cones 9 and I0 toward their apex ends. Near its base cone ID is provided with inlet I1 for compressed air from line I8. Pitch injectors 8 are positioned so that their apex ends project a short distance within tank I.

A conveyor, for example, a rotatable helical screw conveyor I9, is located along the inclined bottom of tank I at the junction of plates 5 and 6, and is adapted to the removal of solid pitch fragments from the bottom of the tank I. Conveyor I9 is rotated by driving means, not shown, attached to wheel 20 by a belt, for example.

Solids removed from tank I by conveyor I 9 are conveniently transported to a point of storage, disposal or use, for example, by a belt conveyor 2 I.

In carrying out our process, hot molten pitch, which typically is withdrawn from a pitching unit such as is described in the before noted copending applications of Harry L. Pelzer and Leroy K. Cheney, is first subjected to a pre-cooling operation.

Pre-cooling may be effected by several means. It is preferred that the step be carried out in a conventional shell and tube heat exchanger using high pressure steam or hot oil as the coolant. It is, however, practicable to cool the pitch in a drop stack using air, steam or water fog as a direct contact coolant. The drop stack method is considered less desirable, primarily as it does not provide a good temperature control. Temperature control in the pre-cooling operation is quite critical as the pitch must not be cooled so close to its softening point that it may clog the pitch injectors which are necessarily cool by conduction of heat to the tank I and its confined coolant.

If a heat exchanger is employed, as in the preferred form, almost any coolant, consistent with the economics involved, will be satisfactory if it is capable of being maintained at a temperature above the softening point of the pitch. Water is not satisfactory. The temperature of cooling water without pressure is too low so that a film of pitch solidifies on the inner surface of the tubes, thereby resulting in poor heat transfer and eventual clogging of the tubes. High pressure steam may be used but advantageously fresh feed to the pitching unit is employed. The pitcher feed will normally arrive at the unit hot or will receive preheat by exchange in the usual manner prior to the exchange with the hot pitch.

5 Also, additional preheat is provided for the feed, assisting the thermal balance of the unit.

The liquid pitch, at the temperatures at which it is withdrawn from the pitching unit, has a density which is less than that of the water in the quench tank. However, as liquid pitch is cooled its density increases and equals and then exceeds that of water before the pitch hardens.

Pitch is typically drawn from a pitching unit at temperatures of about 550 F. to 650F. According to our invention the pitch is pre-cooled to about 350-450 F. in the case of a pitch having a softening point of 282 F. and having a specific gravity of about 1.0 at 550 F. or about 425-550 F. in the case of a pitch having a softening point of 354 F. and having a specific gravity of about 1.0 at 650 F., at which temperatures the pitch has a specific gravity greater than that of water, but is in a free and running condition and not thick and viscous as it would be at temperatures closer to the softening point.

The pre-cooled pitch is delivered without substantial temperature loss to the apparatus pictured in the drawings where it is fed into dispersing nozzles 8 through line [4. At the same time, compressed air is introduced to nozzles 8 by lines 18 e. g., at a rate of approximately 900 standard cubic feet per barrel of pitch injected.

By way of illustration of the pitch injection, a tank about 7 feet high, 8 feet wide and eleven feet long is set up with two pitch nozzles. Water level is maintained two feet from the top of the tank to give a water capacity of about 600 gallons. The pitch nozzles are located 2 feet below the surface of the water and the pitch inlet line I4 in each nozzle is a 1-inch pipe. The compressed airline I8 is a 1 inch pipe and the vertical distance in the annular space between conical surfaces 9 and I is 1 inch. The conical surfaces are each sloped at about 45 angles with their common axis, and surface [0 is truncated at its apex to give a hole [3 of about 1 inches in di ameter.

Pre-cooled liquid pitch is charged to each pitch injector nozzle at a rate of about 5 barrels per hour with an air rate of about 75 standard cubic feet per minute supplied to each injector at 40 p. s. i. g. Water coolant temperature is maintained from 100-120 F. Screw conveyor l9 has a 12 inch screw blade and is rotated at 28 R. P. M. The pitch blown into tank I immediately disperses into small particles, all of which sink and solidify. The particles are easily and readily withdrawn by screw conveyor l9 and all are dense, hard fragments of substantially even size, no larger than 4 inch in diameter. Substantially no fines are produced, and the fragments are readily dried.

When the air rate is decreased to about 35 standard cubic feet per minute, larger, porous particles of pitch are produced, of which a substantial amount, 1. e., float to the surface. A large amount of fines are produced.

When water is used in place of air to disperse the pitch, the results are extremely poor, the pitch produced being in large, porous chunks about 6 to 8 inches in diameter. All of the pitch so quenched is friable, and about to,% of it floats to the top of the tank.

Our process may be carried out at a water temperature in tank I as high as 212 F., the heat from the hot pitch being absorbed by the water evaporation. Under such circumstances 9 gallons of make-up water at 1". are required per barrel 16 6 of pitch treated, but this product is friable and porous.

However, the water temperature'advantageously is maintained at F. or less, in order to obtain a product of greater hardness and density. The cooling water requirement is then approximately 270 gallons of water at 85 F. per barrel of pitch.

While we have shown one means of pitch injection, it is apparent that other means may be used to accomplish the same purpose. For example, it may be desirable to employ a conical directing section around the discharge nozzle to concentrate the zone of high turbulence. However, the injector shown is particularly advantageous as it permits the air stream to surround the stream of liquid pitch and strike it at an angle so as to have a nearly explosive effect, which is essential to the rapid dispersion of the liquid pitch. Moreover, the pitch inlet line does not contact any cool conductor of heat before its immediate point of injection, and is readily accessible if heating is required to prevent clogging during starting conditions or at low rates of operation.

We claim:

1. In the process of cooling and solidifying hot molten petroleum pitch by contact with a water coolant, the steps of simultaneously fragmenting the liquid pitch and dispersing it in a body of the water coolant by injecting liquid pitch at a temperature above the softening point temperature of the pitch but below that at which the specific gravity of the pitch is equal to that of the Water coolant into the body of water coolant beneath the surface thereof, injecting a fluid medi-- um into the molten pitch at the point at which the pitch enters the body of water coolant whereby the pitch is dispersed into fragments in the body of water coolant, solidifying the dispersed fragments of pitch by prolonging the contact thereof with the water coolant, and collecting the solidified fragments of pitch.

2. In the process of claim 1, in which the pitch is dispersed by compressed air.

3. In theprocess of cooling and solidifying hot molten petroleum pitch by contact with a water coolant, the steps of cooling the liquid pitch to a temperature of above the softening point. of the pitch but below the temperature at which the specific gravity of th pitch is equal of that of the' water coolant, simultaneously fragmenting the pre-cooled liquid pitch and dispersing it in a body of the water coolant by injecting the liquid pitch into the body of water coolant beneath the surface thereof, injecting compressed air into the pre-cooled molten pitch at the point at which the pitch enters the body of water coolant whereby the pitch is dispersed into fragments in the body of water coolant, solidifying the dispersed fragments of pitch by prolonging the contact thereof with the water coolant, and collecting the solidifled fragments of pitch.

KENNETH A. SMITH.

DONALD K. HEDEEN.

References Cited in the file or this patent UNITED STATES PATENTS Number Name Date 785,023 Rowley et a1 Mar. 14, 1905 954,451 Merrell Apr. 12, 1910 1,393,383 Linebarser Oct. 11, 1921 

